Zoom lens and imaging apparatus having four lens groups

ABSTRACT

The zoom lens consists of, in order from the object side, a first lens group that has a negative refractive power; a second lens group that has a positive refractive power; a third lens group that has a negative refractive power; and a fourth lens group that has a positive refractive power. During zooming, in each lens group, distances between the adjacent groups in the direction of the optical axis are changed. The first lens group consists of, in order from the object side, a first lens having a negative refractive power, a second lens having a negative refractive power, and a third lens having a positive refractive power. The third lens group consists of a negative lens. During focusing, only the third lens group moves along the optical axis. The zoom lens satisfies predetermined conditional expressions.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a Continuation of U.S. patent application SerNo. 16/108,622 filed Aug. 22, 2018, which claims priority under 35U.S.C. § 119 to Japanese Patent Application No. 2017-161263 filed onAug. 24, 2017. The above application is hereby expressly incorporated byreference, in its entirety, into the present application.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a zoom lens, which is particularlysuitable for imaging apparatuses such as a digital camera, aninterchangeable lens digital camera, and a movie imaging camera, and animaging apparatus comprising the zoom lens.

2. Description of the Related Art

As zoom lenses used for imaging apparatuses such as digital cameras,interchangeable lens digital cameras, and movie imaging cameras, zoomlenses described in JP2015-121768A, JP2014-77867A, and JP2015-4880A areknown.

In the zoom lens used for the imaging apparatuses, there is a demand toachieve reduction in size and weight in order to improve portability. Inaddition, there are demands for high speed focusing, favorable opticalperformance over the entire imaging distance, and an increase in angleof view at the wide-angle end state.

SUMMARY OF THE INVENTION

However, in the zoom lenses disclosed in JP2015-121768A andJP2014-77867A, while a wide angle of view and high speed focusing areachieved, the lens group closest to the object side (the first lensgroup) is large. Thus, it can not be said that reduction in size issufficiently achieved.

In the zoom lens disclosed in JP2015-4880A, it can not be said thatcompatibility with suppression of fluctuation in aberrations caused bythe imaging distance is satisfactorily achieved while achievingreduction in size and high speed focusing.

The present invention has been made in consideration of theabove-mentioned situations, and it is an object of the present inventionto provide a zoom lens which is capable of achieving high opticalperformance over the entire object distance with little fluctuation inaberrations caused by the object distance while being able to performhigh speed focusing with a small size and a lightweight as a whole, andan imaging apparatus comprising the zoom lens.

A first zoom lens of the present invention consists of, in order from anobject side: a first lens group that has a negative refractive power; asecond lens group that has a positive refractive power; a third lensgroup that has a negative refractive power; and a fourth lens group thathas a positive refractive power. During zooming, distances betweenadjacent groups of the first lens group, the second lens group, thethird lens group, and the fourth lens group in a direction of an opticalaxis are changed. The first lens group consists of, in order from theobject side, a first lens having a negative refractive power, a secondlens having a negative refractive power, and a third lens having apositive refractive power. The third lens group consists of a negativelens. During focusing, only the third lens group moves along the opticalaxis. Assuming that a refractive index of the first lens is Nd1, an Abbenumber of the first lens is νd1, a refractive index of the third lens isNd3, an Abbe number of the third lens is νd3, a focal length of thewhole system during focusing on an object at infinity at the wide-angleend is fw, a focal length of the third lens group is f3, a back focallength is Bf, and a maximum image height is IH, Conditional Expressions(1) to (4) are satisfied.1.7<Nd1−0.0037×νd1<2  (1)1.8<Nd3−0.0037×νd3<2  (2)−0.6<fw/f3<−0.15  (3)0.6<Bf/IH<1.2  (4)

A second zoom lens of the present invention consists of, in order froman object side: a first lens group that has a negative refractive power;a second lens group that has a positive refractive power; a third lensgroup that has a negative refractive power; and a fourth lens group thathas a positive refractive power. During zooming, distances betweenadjacent groups of the first lens group, the second lens group, thethird lens group, and the fourth lens group in a direction of an opticalaxis are changed. The first lens group consists of, in order from theobject side, a first lens having a negative refractive power, a secondlens having a negative refractive power, and a third lens having apositive refractive power. The third lens group consists of a negativelens. During focusing, only the third lens group moves along the opticalaxis. Assuming that a refractive index of the first lens is Nd1, an Abbenumber of the first lens is νd1, a refractive index of the third lens isNd3, an Abbe number of the third lens is νd3, a focal length of thewhole system during focusing on an object at infinity at the wide-angleend is fw, a focal length of the third lens group is f3, a back focallength is Bf, and a focal length of the fourth lens group is f4,Conditional Expressions (1) to (3) and (5) are satisfied.1.7<Nd1−0.0037×νd1<2  (1)1.8<Nd3−0.0037×νd3<2  (2)−0.6<fw/f3<−0.15  (3)0.15<Bf/f4<0.35  (5)

In the first and second zoom lenses of the present invention, amongConditional Expression (1-1) to (3-1), it is preferable to satisfy atleast one or more.1.75<Nd1−0.0037×νd1<2  (1-1)1.85<Nd3−0.0037×νd3<2  (2-1)−0.5<fw/f3<−0.2  (3-1)

In the first zoom lens of the present invention, it is preferable tosatisfy Conditional Expression (4-1).0.7<Bf/IH<1.1  (4-1)

In the second zoom lens of the present invention, it is preferable tosatisfy Conditional Expression (5-1).0.18<Bf/f4<0.3  (5-1)

In the first and second zoom lenses of the present invention, it ispreferable that the second lens group has a vibration reduction lensgroup that performs vibration reduction by moving in a directionorthogonal to the optical axis. In addition, assuming that a focallength of the whole system during focusing on an object at infinity atthe telephoto end is ft and a focal length of the vibration reductionlens group is fois, it is preferable to satisfy Conditional Expression(6), and it is more preferable to satisfy Conditional Expression (6-1).0.5<ft/fois<2  (6)1<ft/fois<1.5  (6-1)

It is preferable that the second lens group has a vibration reductionlens group that performs vibration reduction by moving in a directionorthogonal to the optical axis, and it is preferable that the vibrationreduction lens group consists of one lens.

In this case, assuming that an Abbe number of a lens composing thevibration reduction lens group is νud, it is preferable to satisfyConditional Expression (7), and it is more preferable to satisfyConditional Expression (7-1).50<νud<100  (7)55<νud<95  (7-1)

It is preferable that the second lens group has a stop, and has lensesadjacent to the object side and the image side of the stop.

In this case, it is preferable that the second lens group has,successively in order from the object side, a positive lens and thestop.

It is preferable that the second lens group has a cemented lensconsisting of at least one positive lens and at least one negative lenson the image side of the stop.

In this case, it is preferable that the cemented lens consists of onepositive lens and one negative lens. Assuming that a difference (betweenan Abbe number of the positive lens and an Abbe number of the negativelens) between Abbe numbers of the positive lens and the negative lenscomposing the cemented lens is Δνcd, it is preferable to satisfyConditional Expression (8).15<Δνcd<60  (8)

It is preferable that the fourth lens group consists of a positive lens.

The fourth lens group may remain stationary during zooming, and thefourth lens group may move during zooming.

An imaging apparatus of the present invention comprises theabove-mentioned zoom lens of the present invention.

It should be noted that the term “consists of ˜” means that the imaginglens may include not only the above-mentioned elements but also lensessubstantially having no refractive powers, optical elements, which arenot lenses, such as a stop, a mask, a cover glass, and a filter, andmechanism parts such as a lens flange, a lens barrel, an imagingelement, and a camera shaking correction mechanism.

Further, the refractive index and the Abbe number in each conditionalexpression are based on the d line as the reference wavelength.

Further, surface shapes, signs of refractive powers, radii of curvatureof the lenses are assumed as those in paraxial regions in a case wheresome lenses have aspheric surfaces.

According to the first and second zoom lenses of the present invention,the zoom lens consists of, in order from an object side: a first lensgroup that has a negative refractive power; a second lens group that hasa positive refractive power; a third lens group that has a negativerefractive power; and a fourth lens group that has a positive refractivepower. During zooming, distances between adjacent groups of the firstlens group, the second lens group, the third lens group, and the fourthlens group in a direction of an optical axis are changed. The first lensgroup consists of, in order from the object side, a first lens having anegative refractive power, a second lens having a negative refractivepower, and a third lens having a positive refractive power. The thirdlens group consists of a negative lens. During focusing, only the thirdlens group moves along the optical axis. With such a configuration, thezoom lens satisfies predetermined conditional expressions. Therefore, itis possible to provide a zoom lens, which is capable of achieving highoptical performance over the entire object distance with littlefluctuation in aberrations caused by the object distance while beingable to perform high speed focusing with a small size and a lightweightas a whole, and an imaging apparatus comprising the zoom lens.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view illustrating a lens configuration of azoom lens (common to Example 1) according to first and secondembodiments of the present invention.

FIG. 2 is a cross-sectional view illustrating a lens configuration of azoom lens of Example 2 of the present invention.

FIG. 3 is a cross-sectional view illustrating a lens configuration of azoom lens of Example 3 of the present invention.

FIG. 4 is a cross-sectional view illustrating a lens configuration of azoom lens of Example 4 of the present invention.

FIG. 5 is a cross-sectional view illustrating a lens configuration of azoom lens of Example 5 of the present invention.

FIG. 6 is a diagram of aberrations of the zoom lens of Example 1 of thepresent invention during focusing on the object at infinity.

FIG. 7 is a diagram of aberrations of the zoom lens of Example 1 of thepresent invention during focusing on the object at a finite distance.

FIG. 8 is a diagram of aberrations of the zoom lens of Example 2 of thepresent invention during focusing on the object at infinity.

FIG. 9 is a diagram of aberrations of the zoom lens of Example 2 of thepresent invention during focusing on the object at a finite distance.

FIG. 10 is a diagram of aberrations of the zoom lens of Example 3 of thepresent invention during focusing on the object at infinity.

FIG. 11 is a diagram of aberrations of the zoom lens of Example 3 of thepresent invention during focusing on the object at a finite distance.

FIG. 12 is a diagram of aberrations of the zoom lens of Example 4 of thepresent invention during focusing on the object at infinity.

FIG. 13 is a diagram of aberrations of the zoom lens of Example 4 of thepresent invention during focusing on the object at a finite distance.

FIG. 14 is a diagram of aberrations of the zoom lens of Example 5 of thepresent invention during focusing on the object at infinity.

FIG. 15 is a diagram of aberrations of the zoom lens of Example 5 of thepresent invention during focusing on the object at a finite distance.

FIG. 16 is a perspective view illustrating the front side of an imagingapparatus according to an embodiment of the present invention.

FIG. 17 is a perspective view illustrating the rear side of the imagingapparatus of FIG. 16.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, a first embodiment of the present invention will bedescribed with reference to the drawing. FIG. 1 is a cross-sectionalview illustrating a lens configuration of a zoom lens according to afirst embodiment of the present invention. The exemplary configurationshown in FIG. 1 is the same as the configuration of the zoom lens ofExample 1. In FIG. 1, the left side is an object side, and the rightside is an image side. In addition, an aperture stop St shown in thedrawing does not necessarily show its real size and shape, but show aposition on an optical axis Z.

In FIG. 1, aberrations in the wide-angle end state are shown in theupper part indicated by “WIDE”, on-axis rays wa and rays with themaximum angle of view wb are shown as rays. In addition, aberrations inthe telephoto end state are shown in the lower part indicated by “TELE”,and on-axis rays to and rays with the maximum angle of view tb are shownas rays. All of these show a state in which the object at infinity is infocus. In addition, the movement locus of each lens group during zoomingis also shown.

In order to mount the zoom lens on an imaging apparatus, it ispreferable to provide various filters and/or a protective cover glassbased on specification of the imaging apparatus. Thus, FIG. 1 shows anexample where a plane-parallel-plate-like optical member PP, in whichthose are considered, is disposed between the lens system and the imageplane Sim. However, a position of the optical member PP is not limitedto that shown in FIG. 1, and it is also possible to adopt aconfiguration in which the optical member PP is omitted.

The zoom lens of the present embodiment consists of, in order from theobject side: a first lens group G1 that has a negative refractive power;a second lens group G2 that has a positive refractive power; a thirdlens group G3 that has a negative refractive power; and a fourth lensgroup G4 that has a positive refractive power. During zooming, distancesbetween adjacent groups of the first lens group G1, the second lensgroup G2, the third lens group G3, and the fourth lens group G4 in thedirection of the optical axis Z are changed. In such a manner, byproviding the first lens group G1 closest to the object side with anegative refractive power, divergent light is incident into thesucceeding lens group, and there is an advantage in ensuring the amountof peripheral light. Further, by providing the third lens group G3 witha negative refractive power, the rays can be reduced, and there is anadvantage in reducing the diameter.

The first lens group G1 consists of, in order from the object side, afirst lens L1 a having a negative refractive power, a second lens L1 bhaving a negative refractive power, and a third lens L1 c having apositive refractive power. By making an entrance pupil closer to theobject side in the first lens L1 a having a negative refractive power,it contributes to ensuring the angle of view at the wide angle end andreducing the diameter. In addition, by disposing the second lens L1 bhaving a negative refractive power and the third lens L1 c having apositive refractive power successively, it is possible to suppress thespherical aberration at the telephoto end, and to suppress fluctuationin aberrations during zooming in the entire first lens group G1.

The third lens group G3 consists of a negative lens L3 a. Duringfocusing, only the third lens group G3 moves along the optical axis Z.That is, the third lens group G3 functions as a focusing lens groupFOCUS. Such a configuration contributes to reduction in size and weightof the focusing units (a focusing lens group FOCUS and a mechanism formoving the focusing lens group FOCUS) and high-speed autofocus.

Assuming that a refractive index of the first lens L1 a is Nd1, an Abbenumber of the first lens L1 a is νd1, a refractive index of the thirdlens L1 c is Nd3, an Abbe number of the third lens L1 c is νd3, a focallength of the whole system during focusing on an object at infinity atthe wide-angle end is fw, a focal length of the third lens group G3 isf3, a back focal length is Bf, and a maximum image height is IH, thezoom lens is configured to satisfy Conditional Expressions (1) to (4).1.7<Nd1−0.0037×νd1<2  (1)1.8<Nd3−0.0037×νd3<2  (2)−0.6<fw/f3<−0.15  (3)0.6<Bf/IH<1.2  (4)

By not allowing the result of Conditional Expression (1) to be equal toor greater than the upper limit, there is an advantage in correctingchromatic aberration. By not allowing the result of ConditionalExpression (1) to be equal to or less than the lower limit, there is anadvantage in achieving reduction in size and weight. In addition, in acase where Conditional Expression (1-1) is satisfied, it is possible toobtain more favorable characteristics.1.75<Nd1−0.0037×νd1<2  (1-1)

By not allowing the result of Conditional Expression (2) to be equal toor greater than the upper limit, there is an advantage in correctingchromatic aberration. By not allowing the result of ConditionalExpression (2) to be equal to or less than the lower limit, there is anadvantage in achieving reduction in size and weight. In addition, in acase where Conditional Expression (2-1) is satisfied, it is possible toobtain more favorable characteristics.1.85<Nd3−0.0037×νd3<2  (2-1)

By not allowing the result of Conditional Expression (3) to be equal toor greater than the upper limit, it is possible to prevent therefractive power of the third lens group G3 from becoming excessivelyweak. Thus, the amount of movement of the third lens group G3 duringfocusing is minimized. As a result, there is an advantage in achievingreduction in size. By not allowing the result of Conditional Expression(3) to be equal to or less than the lower limit, it is possible toprevent the refractive power of the third lens group G3 from becomingexcessively strong. As a result, there is an advantage in minimizing theamount of fluctuation in aberrations during focusing. In addition, in acase where Conditional Expression (3-1) is satisfied, it is possible toobtain more favorable characteristics.−0.5<fw/f3<−0.2  (3-1)

By not allowing the result of Conditional Expression (4) to be equal toor greater than the upper limit, there is an advantage in reducing thesize thereof. There is an advantage in minimizing the angle of incidenceof the principal ray of off-axis rays to the image plane Sim on thewide-angle side. By not allowing the result of Conditional Expression(4) to be equal to or less than the lower limit, the zoom lens and theimage plane Sim are prevented from becoming excessively close. As aresult, there is an advantage in reducing the diameter of the lens. Inaddition, in a case where Conditional Expression (4-1) is satisfied, itis possible to obtain more favorable characteristics.0.7<Bf/IH<1.1  (4-1)

Next, a second embodiment of the present invention will be described. Alens configuration of the zoom lens according to the second embodimentis the same as that of the zoom lens according to the first embodimentshown in FIG. 1.

The zoom lens of the present embodiment consists of, in order from theobject side: a first lens group G1 that has a negative refractive power;a second lens group G2 that has a positive refractive power; a thirdlens group G3 that has a negative refractive power; and a fourth lensgroup G4 that has a positive refractive power. During zooming, distancesbetween adjacent groups of the first lens group G1, the second lensgroup G2, the third lens group G3, and the fourth lens group G4 in thedirection of the optical axis Z are changed.

The first lens group G1 consists of, in order from the object side, afirst lens L1 a having a negative refractive power, a second lens L1 bhaving a negative refractive power, and a third lens L1 c having apositive refractive power.

The third lens group G3 consists of a negative lens L3 a. Duringfocusing, only the third lens group G3 moves along the optical axis Z.

Assuming that a refractive index of the first lens L1 a is Nd1, an Abbenumber of the first lens L1 a is νd1, a refractive index of the thirdlens L1 c is Nd3, an Abbe number of the third lens L1 c is νd3, a focallength of the whole system during focusing on an object at infinity atthe wide-angle end is fw, a focal length of the third lens group G3 isf3, a back focal length is Bf, and a focal length of the fourth lensgroup G4 is f4, the zoom lens is configured to satisfy ConditionalExpressions (1) to (3) and (5).1.7<Nd1−0.0037×νd1<2  (1)1.8<Nd3−0.0037×νd3<2  (2)−0.6<fw/f3<−0.15  (3)0.15<Bf/f4<0.35  (5)

Compared to the zoom lens according to the first embodiment, the zoomlens according to the second embodiment is configured to satisfyConditional Expression (5) instead of Conditional Expression (4), andthe other configuration is the same. Hence, only Conditional Expression(5) will be described.

By not allowing the result of Conditional Expression (5) to be equal toor greater than the upper limit, it is possible to prevent the backfocal length from becoming excessively long or it is possible to preventthe refractive power of the fourth lens group G4 from becomingexcessively strong. As a result, it is possible to prevent the negativerefractive power of the adjacent third lens group G3 from becomingexcessively strong. Thus, there is an advantage in suppressingfluctuation in aberrations during focusing. By not allowing the resultof Conditional Expression (5) to be equal to or less than the lowerlimit, it is possible to prevent the back focal length from becomingexcessively short or it is possible to prevent the refractive power ofthe fourth lens group G4 from becoming excessively weak. As a result, itis possible to prevent the negative refractive power of the adjacentthird lens group G3 from becoming excessively weak. Thus, the amount ofmovement of the third lens group G3 during focusing is minimized, andthere is an advantage in achieving reduction in size. In addition, in acase where Conditional Expression (5-1) is satisfied, it is possible toobtain more favorable characteristics.0.18<Bf/f4<0.3  (5-1)

In the zoom lens according to the first and second embodiments, thesecond lens group G2 has a vibration reduction lens group OIS thatperforms vibration reduction by moving in the direction orthogonal tothe optical axis Z. Assuming that a focal length of the whole systemduring focusing on an object at infinity at the telephoto end is ft anda focal length of the vibration reduction lens group OIS is fois, it ispreferable to satisfy Conditional Expression (6). By not allowing theresult of Conditional Expression (6) to be equal to or greater than theupper limit, it is possible to prevent the refractive power of thevibration reduction lens group OIS from becoming excessively strong. Asa result, it is possible to reduce fluctuation in aberrations duringvibration reduction. By not allowing the result of ConditionalExpression (6) to be equal to or less than the lower limit, it ispossible to prevent the amount of movement of the vibration reductionlens group OIS from becoming excessively large. Thus, the size of theentire zoom lens and the vibration reduction units (the vibrationreduction lens group OIS and the mechanism for moving the vibrationreduction lens group OIS). In addition, in a case where ConditionalExpression (6-1) is satisfied, it is possible to obtain more favorablecharacteristics.0.5<ft/fois<2  (6)1<ft/fois<1.5  (6-1)

It is preferable that the second lens group G2 has a vibration reductionlens group OIS that performs vibration reduction by moving in adirection orthogonal to the optical axis Z, and it is preferable thatthe vibration reduction lens group OIS consists of one lens. With such aconfiguration, there is an advantage in achieving reduction in size andweight of the vibration reduction unit.

In this case, assuming that an Abbe number of a lens composing thevibration reduction lens group OIS is νud, it is preferable to satisfyConditional Expression (7). By not allowing the result of ConditionalExpression (7) to be equal to or greater than the upper limit, it ispossible to select a material having a sufficient refractive index. Bynot allowing the result of Conditional Expression (7) to be equal to orless than the lower limit, there is an advantage in suppressingfluctuation in chromatic aberration during vibration reduction. Inaddition, in a case where Conditional Expression (7-1) is satisfied, itis possible to obtain more favorable characteristics.50<νud<100  (7)55<νud<95  (7-1)

It is preferable that the second lens group G2 has an aperture stop St,and has lenses adjacent to the object side and the image side of theaperture stop St. With such a configuration, it becomes easy to ensurethe amount of movement of the second lens group G2 during zooming, andthere is an advantage in achieving reduction in size.

In this case, it is preferable that the second lens group G2 has,successively in order from the object side, a positive lens and theaperture stop St. By disposing the positive lens on the object side ofthe aperture stop St in such a manner, there is an advantage inachieving reduction in size of the aperture stop St.

It is preferable that the second lens group G2 has a cemented lensconsisting of at least one positive lens and at least one negative lenson the image side of the aperture stop St. With such a configuration,there is an advantage in correcting longitudinal chromatic aberration.

In this case, it is preferable that the cemented lens consists of onepositive lens and one negative lens. Assuming that a difference (betweenan Abbe number of the positive lens and an Abbe number of the negativelens) between Abbe numbers of the positive lens and the negative lenscomposing the cemented lens is Δνcd, it is preferable to satisfyConditional Expression (8). By satisfying Conditional Expression (8),chromatic aberration in the second lens group G2 can be sufficientlycorrected, and there is an advantage in achieving high opticalperformance. In addition, in a case where Conditional Expression (8-1)is satisfied, it is possible to obtain more favorable characteristics.15<Δνcd<60  (8)20<Δνcd<50  (8-1)

It is preferable that the fourth lens group G4 consists of a positivelens. With such a configuration, it is possible to improve the balanceof fluctuation in aberrations during focusing between the fourth lensgroup G4 and the third lens group G3, which consists of a negative lens,while ensuring the amount of movement of the third lens group G3 duringfocusing.

The fourth lens group G4 may remain stationary during zooming, and thefourth lens group G4 may move during zooming. In a case where the fourthlens group G4 remains stationary during zooming, dust can be preventedfrom entering into the zoom lens. Assuming that the fourth lens group G4is moved during zooming, there is an advantage in reducing the diameterof the fourth lens group G4.

It is preferable that the surface closest to the image side in the firstlens group G1 has a shape convex toward the object side. With such aconfiguration, it becomes easy to ensure a distance between the firstlens group G1 and the second lens group G2 at the telephoto end, andthere is an advantage in achieving reduction in size.

In the example shown in FIG. 1, the optical member PP is disposedbetween the lens system and the image plane Sim. However, variousfilters such as a lowpass filter and a filter for cutting off a specificwavelength region may not be disposed between the lens system and theimage plane Sim. Instead, such various filters may be disposed betweenthe lenses, or coating for functions the same as those of variousfilters may be performed on a lens surface of any lens.

Next, numerical examples of the zoom lens of the present invention willbe described.

First, a zoom lens of Example 1 will be described. FIG. 1 is across-sectional view illustrating a lens configuration of the zoom lensof Example 1. In FIG. 1 and FIGS. 2 to 5 corresponding to Examples 2 to5 to be described later, left sides thereof are the object side, andright sides thereof are the image side. In addition, the aperture stopSt shown in the drawings does not necessarily indicate its size orshape, and indicates a position thereof on the optical axis Z. Further,aberrations in the wide-angle end state are shown in the upper partindicated by “WIDE”, on-axis rays wa and rays with the maximum angle ofview wb are shown as rays. In addition, aberrations in the telephoto endstate are shown in the lower part indicated by “TELE”, and on-axis raysta and rays with the maximum angle of view tb are shown as rays. All ofthese show a state in which the object at infinity is in focus. Inaddition, the movement locus of each lens group during zooming is alsoshown.

The zoom lens of Example 1 is composed of, in order from the objectside, a first lens group G1 composed of three lenses of lenses L1 a toL1 c, a second lens group G2 composed of an aperture stop St and fivelenses L2 a to L2 e, a third lens group G3 composed of only one lens L3a, and a fourth lens group G4 composed of only one lens L4 a. Further,during zooming, the first lens group G1, the second lens group G2, andthe third lens group G3 move, and the fourth lens group G4 remainsstationary.

Table 1 shows basic lens data of the zoom lens of Example 1, Table 2shows data about specification, Table 3 shows data about variablesurface distances, and Table 4 shows data about aspheric surfacecoefficients thereof. Hereinafter, meanings of the reference signs inthe tables are, for example, as described in Example 1, and arebasically the same as those in Examples 2 to 5.

In the lens data of Table 1, the column of the surface number showssurface numbers. The surface of the elements closest to the object sideis the first surface, and the surface numbers sequentially increasetoward the image plane side. The column of the radius of curvature showsradii of curvature of the respective surfaces. The column of the surfacedistance shows distances on the optical axis Z between the respectivesurfaces and the subsequent surfaces. Further, the column of n shows arefractive index of each optical element at the d line (a wavelength of587.6 nm (nanometers)), and the column of νd shows an Abbe number ofeach optical element at the d line (a wavelength of 587.6 nm(nanometers)).

In addition, the sign of the radius of curvature is positive in a casewhere a surface has a shape convex toward the object side, and isnegative in a case where a surface has a shape convex toward the imageplane side. In the basic lens data, the aperture stop St and the opticalmember PP are additionally noted. In a place of a surface number of asurface corresponding to the aperture stop St, the surface number and aterm of (stop) are noted. Further, in the lens data of Table 1, in eachplace of the surface distance which is variable during zooming andfocusing, DD[surface number] is noted. Numerical values eachcorresponding to the DD[surface number] are shown in Table 3.

In the data about the specification of Table 2, in each case of focusingon the object at infinity and focusing on the object at a finitedistance (focusing on the object at a distance of 1m from the imageplane), values of the zoom magnification, the focal length f′, the backfocal length Bf′, the F number FNo., and the total angle of view 2ω(°)are noted.

In the lens data of Table 1, the reference sign * is attached to surfacenumbers of aspheric surfaces, and radii of curvature of the asphericsurfaces are represented by numerical values of paraxial radii ofcurvature. The data about aspheric surface coefficients of Table 4 showsthe surface numbers of the aspheric surfaces and aspheric surfacecoefficients of the aspheric surfaces. The “E±n” (n: an integer) innumerical values of the aspheric surface coefficients of Table 4indicates “×10^(±n)”. The aspheric surface coefficients are values ofthe coefficients KA and Am in aspheric surface expression represented asthe following expression.Zd=C·h ²/{1+(1−KA·C ² ·h ²)^(1/2) }+ΣAm·h ^(m)

Here, Zd is an aspheric surface depth (a length of a perpendicular froma point on an aspheric surface at height h to a plane that isperpendicular to the optical axis and contacts with the vertex of theaspheric surface),

h is a height (a distance from the optical axis),

C is an inverse of a paraxial radius of curvature, and

KA and Am are aspheric surface coefficients, and

Σ at the aspheric surface depth Zd means a sum with respect to m.

In the basic lens data, the data about specification, and the data aboutvariable surface distances, a degree is used as a unit of an angle, andmm (millimeters) is used as a unit of a length, but appropriatedifferent units may be used since the optical system can be used even ina case where the system is enlarged or reduced in proportion.

TABLE 1 Example 1 Lens Data (n and ν are based on d line) Surface Radiusof Surface Number Curvature Distance n ν 1 35.567 0.87 1.95375 32.32 212.500 6.21 *3 −166.657 1.13 1.53409 55.89 *4 38.071 0.45 5 27.460 2.201.94595 17.98 6 83.707 DD[6]  7 12.775 3.12 1.60311 60.64 8 146.879 2.009(Stop) ∞ 1.96 10 15.625 3.76 1.61800 63.33 11 −12.500 0.75 1.6727032.10 12 22.574 0.37 *13 46.279 0.62 1.88202 37.22 *14 20.056 1.25 1528.405 1.62 1.51633 64.14 16 −62.961 DD[16] *17 −19.477 0.83 1.5163364.06 *18 185.962 DD[18] 19 68.556 3.12 1.89190 37.13 20 −124.994 7.1921 ∞ 2.85 1.51633 64.14 22 ∞ DD[22]

TABLE 2 Example 1 Specification (d Line) Focusing on Object at InfinityWIDE MID TELE Zoom Magnification 1.0 1.7 2.8 f′ 15.46 26.01 43.76 Bf′11.48 11.48 11.48 FNo. 3.56 4.22 5.76 2ω[°] 93.2 57.4 34.6 Focusing onObject at Finite Distance WIDE MID TELE Zoom Magnification 1.0 1.7 2.8f′ 15.39 25.80 43.12 Bf′ FNo. 3.57 4.24 5.80 2ω[°] 93.0 57.0 34.2

TABLE 3 Example 1 Moved Surface Distance Focusing on Object at InfinityWIDE MID TELE DD[6] 23.03 9.72 0.39 DD[16] 1.78 4.47 10.98 DD[18] 7.0913.52 18.32 DD[22] 2.41 2.41 2.41 Focusing on Object at Finite DistanceWIDE MID TELE DD[6] 23.03 9.72 0.39 DD[16] 2.01 4.96 12.14 DD[18] 6.8713.04 17.16 DD[22] 2.41 2.41 2.41

TABLE 4 Example 1 Aspheric surface coefficient Surface Number 3 4 13 KA1.0000000E+00 1.0000000E+00 1.0000000E+00 A3 0.0000000E+00 0.0000000E+000.0000000E+00 A4 −1.0819127E−06  −3.3952932E−05  8.5098274E−05 A5−2.7488812E−05  −1.4238550E−05  −2.1605954E−04  A6 7.4995863E−063.0228297E−06 4.8035406E−05 A7 −7.4607015E−07  −2.1440511E−08 3.9492842E−06 A8 4.6610516E−09 −3.8153342E−08  −2.6191475E−06  A93.0046511E−09 4.5511579E−10 1.0747465E−07 A10 6.2089220E−113.1775888E−10 2.8434370E−08 A11 −6.3379780E−12  1.1477360E−118.1291461E−09 A12 −2.4856103E−12  −1.9466172E−12  −2.9346471E−10  A137.9952646E−14 −1.9010929E−13  2.3142358E−10 A14 8.8179053E−159.6733898E−17 −1.4036485E−10  A15 6.0132523E−16 9.0411570E−16−4.2763386E−11  A16 −7.0790962E−17  9.8969392E−17 3.2611479E−12 A17−1.2696757E−18  5.5661862E−18 1.0713169E−12 A18 3.4642064E−20−6.2944607E−19  3.4062175E−13 A19 2.5015608E−21 −1.3072020E−19 1.0842981E−14 A20 3.0930873E−22 8.4295392E−21 −1.3785869E−14  SurfaceNumber 14 17 18 KA 1.0000000E+00 1.0000000E+00 1.0000000E+00 A30.0000000E+00 0.0000000E+00 0.0000000E+00 A4 1.5046514E−04 5.7641026E−048.1004504E−04 A5 −1.2516791E−04  −2.7728125E−05  −1.9325677E−04  A62.4421887E−05 −3.4579663E−05  1.7703556E−05 A7 −5.9473522E−06 5.3393233E−06 2.1921002E−07 A8 2.2055101E−06 7.5317973E−07 3.8441652E−08A9 1.4547064E−07 −5.2588119E−08  2.3388266E−09 A10 −6.3015199E−08 −2.8797238E−08  4.4167732E−10 A11 −2.4112190E−08  −4.8567333E−10 −1.5401166E−09  A12 −2.5506144E−11  3.4857371E−10 −1.5864859E−10  A134.3154271E−10 5.8918446E−12 1.7299766E−11 A14 2.8773343E−108.0798376E−12 9.6678206E−12 A15 8.6474993E−12 −2.8705432E−13 1.4745553E−12 A16 −6.7223012E−12  2.5937199E−13 −2.9769134E−13  A17−3.4492574E−12  −5.1917695E−14  −3.2894801E−14  A18 1.8172586E−13−3.6107148E−15  −1.3045407E−15  A19 1.7824842E−13 −6.3184282E−16 1.2657422E−15 A20 −2.0542773E−14  1.6925973E−16 −7.0673211E−17 

FIG. 6 shows aberration diagrams aberrations of the zoom lens of Example1 during focusing on the object at infinity. FIG. 7 shows aberrationdiagrams of the zoom lens of Example 1 during focusing on the object ata finite distance (focusing on the object at a distance of 1 m from theimage plane). In addition, spherical aberration, astigmatism,distortion, and lateral chromatic aberration at the wide-angle end(WIDE) are shown in order from the upper left side of FIG. 6 or 7,spherical aberration, astigmatism, distortion, and lateral chromaticaberration at the middle position (MID) are shown in order from themiddle left side of FIG. 6 or 7, and spherical aberration, astigmatism,distortion, and lateral chromatic aberration at the telephoto end (TELE)are shown in order from the lower left side of FIG. 6 or 7. Theaberration diagrams illustrating spherical aberration, astigmatism, anddistortion indicate aberrations that occur in a case where the d line (awavelength of 587.6 nm (nanometers)) is set as a reference wavelength.In the spherical aberration diagram, aberrations at the d line (awavelength of 587.6 nm (nanometers)), the C line (a wavelength of 656.3nm (nanometers)), the F line (a wavelength of 486.1 nm (nanometers)),and the g line (a wavelength of 435.8 nm (nanometers)) are respectivelyindicated by the solid line, the long dashed line, the short dashedline, and the gray solid line. In the astigmatism diagram, aberrationsin sagittal and tangential directions are respectively indicated by thesolid line and the short dashed line. In the lateral chromaticaberration diagram, aberrations at the C line (a wavelength of 656.3 nm(nanometers)), the F line (a wavelength of 486.1 nm (nanometers)), andthe g line (a wavelength of 435.8 nm (nanometers)) are respectivelyindicated by the long dashed line, the short dashed line, and the graysolid line. In addition, in the spherical aberration diagram, FNo. meansan F number. In the other aberration diagrams, ω means a half angle ofview.

Next, a zoom lens of Example 2 will be described. FIG. 2 is across-sectional view illustrating a lens configuration of the zoom lensof Example 2. The group configuration of the zoom lens of Example 2 andthe lens groups moving during zooming are the same as those of the zoomlens of Example 1. Table 5 shows basic lens data of the zoom lens ofExample 2, Table 6 shows data about specification, Table 7 shows dataabout surface distances which are variable, Table 8 shows data aboutaspheric surface coefficients thereof, FIG. 8 shows aberration diagramsduring focusing on the object at infinity, and FIG. 9 shows aberrationdiagrams during focusing on the object at a finite distance (focusing onthe object at a distance of 1 m from the image plane).

TABLE 5 Example 2 Lens Data (n and ν are based on d line) Surface Radiusof Surface Number Curvature Distance n ν 1 41.857 2.03 1.91082 35.25 212.500 6.21 *3 −170.254 1.50 1.51633 64.06 *4 52.263 0.50 5 31.484 2.211.94595 17.98 6 98.598 DD[6]  7 12.789 2.50 1.60311 60.64 8 279.980 2.009(Stop) ∞ 1.83 10 15.625 3.51 1.61800 63.33 11 −14.666 0.75 1.6727032.10 12 17.176 0.45 *13 37.193 0.79 1.88202 37.22 *14 18.961 1.25 1534.873 1.62 1.51633 64.14 16 −59.527 DD[16] *17 −16.616 0.75 1.5163364.06 *18 −38.930 DD[18] 19 89.842 3.12 1.89190 37.13 20 −124.995 7.1921 ∞ 2.85 1.51633 64.14 22 ∞ DD[22]

TABLE 6 Example 2 Specification (d Line) Focusing on Object at InfinityWIDE MID TELE Zoom Magnification 1.0 1.7 2.8 f′ 15.46 26.01 43.76 Bf′11.48 11.48 11.48 FNo. 3.56 4.15 5.76 2ω[°] 93.2 58.0 35.0 Focusing onObject at Finite Distance WIDE MID TELE Zoom Magnification 1.0 1.7 2.8f′ 15.40 25.84 43.27 Bf′ FNo. 3.57 4.17 5.81 2ω[°] 93.0 57.6 34.8

TABLE 7 Example 2 Moved Surface Distance Focusing on Object at InfinityWIDE MID TELE DD[6] 22.71 9.54 0.60 DD[16] 1.75 4.05 11.11 DD[18] 7.4915.09 21.08 DD[22] 2.41 2.41 2.41 Focusing on Object at Finite DistanceWIDE MID TELE DD[6] 22.71 9.54 0.60 DD[16] 2.14 4.86 13.00 DD[18] 7.1014.28 19.19 DD[22] 2.41 2.41 2.41

TABLE 8 Example 2 Aspheric surface coefficient Surface Number 3 4 13 KA1.0000000E+00 1.0000000E+00 1.0000000E+00 A3 0.0000000E+00 0.0000000E+000.0000000E+00 A4 2.3102402E−05 −1.9872664E−05  4.4258136E−05 A5−3.0605318E−05  −1.5575712E−05  −2.1804482E−04  A6 7.5843999E−062.8877488E−06 4.8891699E−05 A7 −7.4650433E−07  −1.9432425E−08 4.1088326E−06 A8 4.5517244E−09 −3.7588737E−08  −2.6397640E−06  A93.0198780E−09 4.8989472E−10 1.1276074E−07 A10 6.4361175E−113.1874744E−10 2.8066116E−08 A11 −6.1999295E−12  1.1436966E−118.2174220E−09 A12 −2.4847556E−12  −1.9563157E−12  −4.2633115E−10  A137.9141628E−14 −1.9124501E−13  2.1648624E−10 A14 8.7287405E−159.4384614E−18 −1.4118345E−10  A15 5.9237115E−16 8.9693400E−16−4.2814363E−11  A16 −7.1495434E−17  9.8425587E−17 3.5861675E−12 A17−1.2834068E−18  5.5344444E−18 1.0882290E−12 A18 3.5072366E−20−6.3006156E−19  3.5904977E−13 A19 2.5933437E−21 −1.3047190E−19 1.1031178E−14 A20 3.3001880E−22 8.4934016E−21 −1.4829709E−14  SurfaceNumber 14 17 18 KA 1.0000000E+00 1.0000000E+00 1.0000000E+00 A30.0000000E+00 0.0000000E+00 0.0000000E+00 A4 1.0944202E−04 6.4736442E−048.5492381E−04 A5 −1.2878047E−04  −1.8223142E−05  −1.8615203E−04  A62.4956726E−05 −3.4670275E−05  1.8120470E−05 A7 −5.6244517E−06 5.2443248E−06 1.9097969E−07 A8 2.3172252E−06 7.5375711E−07 2.1447225E−08A9 1.2812149E−07 −5.5776127E−08  −1.7277950E−09  A10 −6.6704772E−08 −2.8409393E−08  1.7554165E−09 A11 −2.4807429E−08  −4.6872033E−10 −1.6619831E−09  A12 −5.4431427E−11  3.7188422E−10 −1.7204532E−10  A134.4891893E−10 1.0993389E−12 1.6563486E−11 A14 2.8921689E−107.3895099E−12 9.7918978E−12 A15 1.0335906E−11 −4.5018064E−13 1.5370010E−12 A16 −6.4045677E−12  2.8069880E−13 −2.8438703E−13  A17−3.4791030E−12  −4.9341085E−14  −3.3897996E−14  A18 1.8259527E−13−2.3889181E−15  −1.4774817E−15  A19 1.7713453E−13 −6.0215416E−16 1.2373185E−15 A20 −2.0982766E−14  1.3744628E−16 −6.7198913E−17 

Next, a zoom lens of Example 3 will be described. FIG. 3 is across-sectional view illustrating a lens configuration of the zoom lensof Example 3. The group configuration of the zoom lens of Example 3 andthe lens groups moving during zooming are the same as those of the zoomlens of Example 1. Table 9 shows basic lens data of the zoom lens ofExample 3, Table 10 shows data about specification, Table 11 shows dataabout surface distances which are variable, Table 12 shows data aboutaspheric surface coefficients thereof, FIG. 10 shows aberration diagramsduring focusing on the object at infinity, and FIG. 11 shows aberrationdiagrams during focusing on the object at a finite distance (focusing onthe object at a distance of 1 m from the image plane).

TABLE 9 Example 3 Lens Data (n and ν are based on d line) Surface Radiusof Surface Number Curvature Distance n ν 1 33.295 1.50 1.95375 32.32 212.545 6.80 *3 −166.671 1.25 1.53409 55.89 *4 37.868 0.62 5 28.348 2.421.94595 17.98 6 77.488 DD[6]  7 14.050 3.25 1.62041 60.29 8 220.173 2.009(Stop) ∞ 1.41 10 16.454 3.51 1.53775 74.70 11 −16.454 0.88 1.6258835.70 12 11.479 0.29 *13 8.654 0.85 1.58313 59.38 *14 9.675 2.00 1525.665 2.14 1.49700 81.61 16 −54.915 DD[16] *17 −23.396 0.75 1.5831359.38 *18 538.989 DD[18] 19 199.780 3.13 1.80400 46.53 20 −55.566 7.3321 ∞ 2.85 1.51633 64.14 22 ∞ DD[22]

TABLE 10 Example 3 Specification (d Line) Focusing on Object at InfinityWIDE MID TELE Zoom Magnification 1.0 1.7 2.9 f′ 15.33 25.78 43.72 Bf′11.62 11.62 11.62 FNo. 3.58 4.22 5.76 2ω[°] 92.4 57.6 34.6 Focusing onObject at Finite Distance WIDE MID TELE Zoom Magnification 1.0 1.7 2.9f′ 15.25 25.57 43.04 Bf′ FNo. 3.58 4.24 5.79 2ω[°] 92.2 57.2 34.4

TABLE 11 Example 3 Moved Surface Distance Focusing on Object at InfinityWIDE MID TELE DD[6] 24.57 10.26 0.34 DD[16] 2.38 5.33 12.39 DD[18] 7.1313.30 18.25 DD[22] 2.41 2.41 2.41 Focusing on Object at Finite DistanceWIDE MID TELE DD[6] 24.57 10.26 0.34 DD[16] 2.63 5.87 13.68 DD[18] 6.8812.76 16.96 DD[22] 2.41 2.41 2.41

TABLE 12 Example 3 Aspheric surface coefficient Surface Number 3 4 13 KA1.0000000E+00 1.0000000E+00 1.0000000E+00 A3 0.0000000E+00 0.0000000E+000.0000000E+00 A4 −1.9140163E−05  −8.9669372E−05  −5.7885505E−05  A5−2.0582766E−05  1.2120440E−05 −4.5028218E−05  A6 8.7532733E−06−1.2563822E−07  3.0080467E−05 A7 −1.2534038E−06  −6.0303929E−08 −5.6206804E−06  A8 4.0773420E−08 −2.5960056E−08  −3.4363745E−06  A94.0704728E−09 2.0308435E−09 6.7064995E−07 A10 −9.4877383E−13 3.0865462E−10 1.2992400E−07 A11 −1.3786661E−11  2.5785525E−125.4385873E−09 A12 −2.3438579E−12  −2.7120098E−12  −8.1095113E−09  A137.0378998E−14 −2.3213883E−13  −1.0069337E−09  A14 4.7956714E−155.5221688E−16 −1.5186113E−10  A15 6.5570093E−16 1.5262265E−152.7601121E−11 A16 −6.1312681E−17  1.3658555E−16 1.8124262E−11 A17−3.1119018E−19  6.8029137E−18 6.8738032E−12 A18 4.4360739E−19−7.0655118E−19  −1.1634526E−12  A19 8.8956009E−21 −1.5783086E−19 −3.5841100E−13  A20 −2.7150711E−21  8.6449700E−21 5.1481080E−14 SurfaceNumber 14 17 18 KA 1.0000000E+00 1.0000000E+00 1.0000000E+00 A30.0000000E+00 0.0000000E+00 0.0000000E+00 A4 2.4485462E−04 8.7676592E−048.4593296E−04 A5 −1.4110635E−04  −1.2912489E−04  −1.0174404E−04  A65.6570853E−05 −1.1057738E−05  −1.0893908E−05  A7 −1.2286182E−05 3.5517914E−06 1.6115318E−06 A8 3.1442298E−07 3.9148966E−07 3.6642342E−07A9 4.9931822E−08 −5.1672445E−08  −6.6077822E−09  A10 −2.6354143E−08 −2.3030362E−08  1.3845027E−09 A11 −4.8123943E−09  8.0622832E−10−2.6787740E−09  A12 4.7006529E−09 4.6251920E−10 −2.5830497E−10  A137.8000672E−10 −1.0569499E−11  2.4784233E−11 A14 2.4725126E−104.2888450E−12 1.4336896E−11 A15 −1.1394066E−10  −1.9088366E−12 2.0857507E−12 A16 −3.3900876E−11  3.0620564E−13 −3.4550528E−13  A17−3.6498853E−12  −3.4565295E−14  −5.5890953E−14  A18 2.0945668E−123.2062861E−15 −2.8207885E−15  A19 7.3243178E−13 −8.4800996E−16 2.0201792E−15 A20 −1.4616295E−13  8.6893598E−17 −1.1386512E−16 

Next, a zoom lens of Example 4 will be described. FIG. 4 is across-sectional view illustrating a lens configuration of the zoom lensof Example 4. The group configuration of the zoom lens of Example 4 andthe lens groups moving during zooming are the same as those of the zoomlens of Example 1. Table 13 shows basic lens data of the zoom lens ofExample 4, Table 14 shows data about specification, Table 15 shows dataabout surface distances which are variable, Table 16 shows data aboutaspheric surface coefficients thereof, FIG. 12 shows aberration diagramsduring focusing on the object at infinity, and FIG. 13 shows aberrationdiagrams during focusing on the object at a finite distance (focusing onthe object at a distance of 1 m from the image plane).

TABLE 13 Example 4 Lens Data (n and ν are based on d line) SurfaceRadius of Surface Number Curvature Distance n ν 1 37.234 0.95 1.9537532.32 2 12.500 5.92 *3 −284.651 1.00 1.53409 55.89 *4 39.025 0.50 526.405 2.40 1.94595 17.98 6 71.780 DD[6]  7 12.931 2.76 1.60311 60.64 895.540 2.13 9(Stop) ∞ 2.13 10 16.604 3.51 1.61800 63.33 11 −14.619 0.691.67270 32.10 12 22.534 0.40 *13 36.231 0.62 1.88202 37.22 *14 20.7111.25 15 29.737 1.62 1.51633 64.14 16 −52.105 DD[16] *17 −21.414 0.691.58313 59.38 *18 162.838 DD[18] 19 71.162 3.12 1.83481 42.74 20−124.995 11.69  21 ∞ 2.85 1.51633 64.14 22 ∞ DD[22]

TABLE 14 Example 4 Specification (d Line) Focusing on Object at InfinityWIDE MID TELE Zoom Magnification 1.0 1.7 2.8 f′ 15.47 26.02 43.78 Bf′14.70 14.70 14.70 FNo. 3.56 4.21 5.76 2ω[°] 93.2 58.0 35.0 Focusing onObject at Finite Distance WIDE MID TELE Zoom Magnification 1.0 1.7 2.8f′ 15.39 25.76 42.98 Bf′ FNo. 3.57 4.23 5.80 2ω[°] 93.0 57.6 34.6

TABLE 15 Example 4 Moved Surface Distance Focusing on Object at InfinityWIDE MID TELE DD[6] 23.87 9.70 0.39 DD[16] 1.83 4.99 10.95 DD[18] 4.8410.71 16.87 DD[22] 1.13 1.13 1.13 Focusing on Object at Finite DistanceWIDE MID TELE DD[6] 23.87 9.70 0.39 DD[16] 2.04 5.45 11.98 DD[18] 4.6310.26 15.83 DD[22] 1.13 1.13 1.13

TABLE 16 Example 4 Aspheric surface coefficient Surface Number 3 4 13 KA1.0000000E+00 1.0000000E+00 1.0000000E+00 A3 0.0000000E+00 0.0000000E+000.0000000E+00 A4 7.2543638E−06 −2.6792194E−05  1.0153410E−04 A5−2.6740525E−05  −1.3809102E−05  −2.1614739E−04  A6 7.4822053E−063.0144481E−06 4.7805353E−05 A7 −7.4665485E−07  −2.2060881E−08 3.9186524E−06 A8 4.7229072E−09 −3.8176199E−08  −2.5866656E−06  A93.0075226E−09 4.5275216E−10 1.0982577E−07 A10 6.2080009E−113.1756049E−10 2.8857763E−08 A11 −6.3243924E−12  1.1465233E−118.1427116E−09 A12 −2.4850129E−12  −1.9473382E−12  −2.9736430E−10  A138.0419436E−14 −1.9014716E−13  2.3113804E−10 A14 8.8124842E−158.1969666E−17 −1.4130071E−10  A15 6.0094430E−16 9.0235118E−16−4.3001217E−11  A16 −7.0733966E−17  9.8768185E−17 3.1733889E−12 A17−1.2852645E−18  5.5436632E−18 1.0668616E−12 A18 3.2661649E−20−6.3178638E−19  3.3926052E−13 A19 2.2420068E−21 −1.3095242E−19  1.1262584E−14  A20 2.6378131E−22 8.4066924E−21 −1.3598628E−14  Surface Number14 17 18 KA 1.0000000E+00 1.0000000E+00 1.0000000E+00 A3 0.0000000E+000.0000000E+00 0.0000000E+00 A4 1.4179500E−04 5.9161845E−04 8.2242216E−04A5 −1.2397788E−04  −2.5914484E−05  −1.9231298E−04  A6 2.4342531E−05−3.4438878E−05  1.7878431E−05 A7 −6.0032094E−06  5.3377134E−062.4615950E−07 A8 2.2340007E−06 7.5589025E−07 3.4837013E−08 A91.4487974E−07 −5.3228108E−08  1.0042287E−09 A10 −6.2753506E−08 −2.9220329E−08  −3.3265004E−10  A11 −2.4291246E−08  −5.8709293E−10 −1.4951082E−09  A12 −5.1651402E−11  3.2437211E−10 −1.5798047E−10  A134.2994810E−10 2.7232638E−12 1.7045793E−11 A14 2.8924537E−101.0562710E−11 1.0099131E−11 A15 8.8793125E−12 −4.0411353E−13 1.5099117E−12 A16 −6.7432630E−12  3.2482397E−13 −2.9004804E−13  A17−3.4371478E−12  −5.2122069E−14  −3.6414197E−14  A18 1.8149763E−13−6.8919262E−15  −1.2249800E−15  A19 1.7801472E−13 −4.2922593E−16 1.2984660E−15 A20 −2.0676419E−14  1.7614142E−16 −7.4672483E−17 

Next, a zoom lens of Example 5 will be described. FIG. 5 is across-sectional view illustrating a lens configuration of the zoom lensof Example 5. The group configuration of the zoom lens of Example 5 isthe same as that of the zoom lens of Example 1. However, theconfiguration is made such that all the lens groups of the first lensgroup G1, the second lens group G2, the third lens group G3, and thefourth lens group G4 move during zooming. Table 17 shows basic lens dataof the zoom lens of Example 5, Table 18 shows data about specification,Table 19 shows data about surface distances which are variable, Table 20shows data about aspheric surface coefficients thereof, FIG. 14 showsaberration diagrams during focusing on the object at infinity, and FIG.15 shows aberration diagrams during focusing on the object at a finitedistance (focusing on the object at a distance of 1 m from the imageplane).

TABLE 17 Example 5 Lens Data (n and ν are based on d line) SurfaceRadius of Surface Number Curvature Distance n ν 1 23.877 2.05 2.0010029.13 2 11.905 6.75 *3 −476.708 1.50 1.53586 56.06 *4 27.069 0.50 520.726 2.12 1.95906 17.47 6 37.252 DD[6]  *7 11.490 3.12 1.76450 49.10*8 54.267 1.61 9(Stop) ∞ 0.50 10 16.129 3.51 1.49700 81.61 11 −10.1470.75 1.80610 33.27 12 29.173 1.12 *13 −8.633 0.82 1.88385 37.20 *14−10.047 0.87 15 26.134 1.57 1.52638 60.20 16 −54.939 DD[16] 17 −46.1320.74 1.59551 39.22 18 36.715 DD[18] 19 47.127 3.12 1.95375 32.32 20 ∞DD[20] 21 ∞ 2.85 1.51633 64.14 22 ∞ DD[22]

TABLE 18 Example 5 Specification (d Line) Focusing on Object at InfinityWIDE MID TELE Zoom Magnification 1.0 1.7 3.0 f′ 16.45 27.67 48.53 Bf′13.32 22.82 39.06 FNo. 3.57 4.62 5.77 2ω[°] 89.8 56.0 32.8 Focusing onObject at Finite Distance WIDE MID TELE Zoom Magnification 1.0 1.7 3.0f′ 16.35 27.38 47.68 Bf′ FNo. 3.58 4.66 5.92 2ω[°] 89.6 55.6 32.0

TABLE 19 Example 5 Moved Surface Distance Focusing on Object at InfinityWIDE MID TELE DD[6] 23.99 9.54 0.34 DD[16] 3.25 3.40 4.53 DD[18] 4.924.92 4.92 DD[20] 9.06 18.57 34.81 DD[22] 2.38 2.38 2.38 Focusing onObject at Finite Distance WIDE MID TELE DD[6] 23.99 9.54 0.34 DD[16]3.53 3.98 5.90 DD[18] 4.64 4.34 3.55 DD[20] 9.06 18.57 34.81 DD[22] 2.382.38 2.38

TABLE 20 Example 5 Aspheric surface coefficient Surface Number 3 4 7 KA1.0000000E+00 1.0000000E+00 1.0000000E+00 A3 0.0000000E+00 0.0000000E+000.0000000E+00 A4 −1.2479530E−05  −5.1298041E−05  7.7147143E−05 A5−3.0316220E−05  −1.2965016E−05  −2.6385146E−05  A6 8.1777812E−062.6033380E−06 7.7523908E−06 A7 −7.7340575E−07  1.0770292E−07−4.6734700E−07  A8 5.4625150E−09 −3.8809505E−08  −4.4154284E−08  A93.3452881E−09 −3.7835635E−10  6.5528241E−09 A10 3.1971022E−112.5368943E−10 1.9027167E−09 A11 −1.1589373E−11  1.2059422E−112.2960060E−12 A12 −2.7993715E−12  −1.7620815E−12  8.1500169E−12 A139.9664751E−14 −1.2627438E−13  −6.4020028E−12  A14 1.3558699E−144.0908393E−15 −7.4285402E−13  A15 1.1168514E−15 9.7401150E−162.6483395E−14 A16 −5.8423449E−17  8.2346673E−17 5.4557374E−15 A17−3.7971760E−18  1.9525918E−18 3.1331559E−15 A18 −4.2047649E−19 −9.9014622E−19  5.8332642E−16 A19 −2.7055286E−20  −1.3344325E−19 1.6786304E−17 A20 4.3481825E−21 1.1644509E−20 −1.6461745E−17  A210.0000000E+00 Surface Number 8 13 14 KA 1.0000000E+00 1.0000000E+00 1.0000000E+00 A3 0.0000000E+00 0.0000000E+00  0.0000000E+00 A41.1037934E−04 1.1444595E−03  1.1919682E−03 A5 −7.1122564E−05 3.5962827E−05 −1.2558675E−04 A6 2.4506177E−05 1.0123736E−05 8.8635425E−05 A7 −1.5338888E−06  5.0340715E−06 −1.1365084E−05 A8−3.3192903E−07  −6.8463693E−07  −5.5198713E−07 A9 2.6004908E−09−3.5821916E−08   1.0649835E−07 A10 8.0860435E−09 −2.8368475E−08  3.7195016E−08 A11 1.1450405E−09 5.4375290E−09 −9.9831982E−11 A127.1485033E−11 −4.9487739E−10   1.4809940E−09 A13 −2.2322148E−11 5.8968748E−10 −9.5662707E−11 A14 −7.7361700E−12  −1.1217296E−10 −5.6300371E−11 A15 −6.2077819E−13  −3.4163229E−11  −2.1563359E−11 A166.6666894E−15 2.7548335E−13 −7.0897114E−12 A17 2.3471469E−141.0592286E−12 −1.5829873E−12 A18 5.7497842E−15 2.8216735E−13 6.7727584E−13 A19 7.6310698E−16 6.3675693E−15  2.3045500E−13 A20−2.2242802E−16  −1.0458495E−14  −4.4001412E−14 A21 0.0000000E+00

Table 21 shows values corresponding to Conditional Expressions (1) to(8) of the zoom lenses of Examples 1 to 5. It should be noted that, inthe above-mentioned examples, the d line is set as the referencewavelength, and the values shown in Table 21 are values at the referencewavelength.

TABLE 21 Expres- sion Conditional Exam- Exam- Exam- Exam- Exam- NumberExpression ple 1 ple 2 ple 3 ple 4 ple 5 (1) Nd1 − 1.83 1.78 1.83 1.831.89 0.0037 × νd1 (2) Nd3 − 1.88 1.88 1.88 1.88 1.89 0.0037 × νd3 (3)fw/f3 −0.45 −0.27 −0.40 −0.48 −0.48 (4) Bf/IH 0.74 0.74 0.76 0.95 0.81(5) Bf/f4 0.23 0.19 0.21 0.27 0.27 (6) ft/fois 1.15 1.02 1.23 1.19 1.43(7) νud 64.14 81.61 81.61 64.14 60.20 (8) Δνcd 31.23 31.23 39.00 31.2348.34

As can be seen from the above data, all the zoom lenses of Examples 1 to5 are zoom lenses each of which satisfies Conditional Expressions (1) to(8), and each of which is capable of achieving high optical performanceover the entire object distance with little fluctuation in aberrationscaused by the object distance while being able to perform high speedfocusing with a small size and a lightweight as a whole.

Next, an embodiment of the imaging apparatus according to the presentinvention will be described with reference to FIGS. 16 and 17. In FIGS.16 and 17, a camera 30, which is obliquely viewed respectively on thefront side and the rear side, is a non-reflex (so-called mirrorless)type digital camera on which an interchangeable lens 20 housing the zoomlens 1 according to the above-mentioned embodiment of the presentinvention in a lens barrel is detachably mounted.

The camera 30 comprises a camera body 31, and a shutter button 32 and apower button 33 are provided on an upper surface thereof. Further,operation sections 34 and 35 and a display section 36 are provided on arear surface of the camera body 31. The display section 36 is fordisplaying a captured image and an image within an angle of view beforeimaging.

An imaging aperture, through which light from an imaging target isincident, is provided at the center on the front surface of the camerabody 31. A mount 37 is provided at a position corresponding to theimaging aperture. The interchangeable lens 20 is mounted on the camerabody 31 with the mount 37 interposed therebetween.

In the camera body 31, there are provided an imaging element (not shownin the drawing), a signal processing circuit, a recording medium, andthe like. The imaging element such as a charge coupled device (CCD)outputs a captured image signal based on a subject image which is formedthrough the interchangeable lens 20. The signal processing circuitgenerates an image through processing of the captured image signal whichis output from the imaging element. The recording medium records thegenerated image. The camera 30 is able to capture a still image or amoving image by pressing the shutter button 32, and is able to storeimage data, which is obtained through imaging, in the storage medium.

The present invention has been hitherto described through embodimentsand examples, but the present invention is not limited to theabove-mentioned embodiments and examples, and may be modified intovarious forms. For example, values such as the radius of curvature, thesurface distance, the refractive index, and the Abbe number of each lenscomponent are not limited to the values shown in the examples, anddifferent values may be used therefor.

In the above-mentioned embodiment of the imaging apparatus, thenon-reflex type digital camera is taken as an example and described withthe drawings. However, the imaging apparatus of the present invention isnot limited to this. For example, the present invention may be appliedto imaging apparatuses such as video cameras, digital cameras which arenot the non-reflex type, movie imaging cameras, broadcast cameras.

EXPLANATION OF REFERENCES

-   -   1: zoom lens    -   20: interchangeable lens    -   30: camera    -   31: camera body    -   32: shutter button    -   33: power button    -   34, 35: operation section    -   36: display section    -   37: mount    -   FOCUS: focusing lens group    -   G1: first lens group    -   G2: second lens group    -   G3: third lens group    -   G4: fourth lens group    -   L1 a to L4 a: lens    -   OIS: vibration reduction lens group    -   PP: optical member    -   Sim: image plane    -   St: aperture stop    -   ta: on-axis rays at wide-angle end    -   tb: rays with the maximum angle of view at telephoto end    -   wa: on-axis rays at wide-angle end    -   wb: rays with the maximum angle of view at wide-angle end    -   Z: optical axis

What is claimed is:
 1. A zoom lens consisting of, in order from anobject side: a first lens group that has a negative refractive power; asecond lens group that has a positive refractive power; a third lensgroup that has a negative refractive power; and a fourth lens group thathas a positive refractive power, wherein during zooming, distancesbetween adjacent groups of the first lens group, the second lens group,the third lens group, and the fourth lens group in a direction of anoptical axis are changed, wherein the third lens group consists of anegative lens, wherein during focusing, only the third lens group movesalong the optical axis, wherein assuming that a back focal length at thewide-angle end is Bf, and a focal length of the fourth lens group is f4,Conditional Expression (5-2) is satisfied0.21≤Bf/f4<0.3  (5-2), wherein the second lens group has a stop, and haslenses adjacent to the object side and the image side of the stop,wherein the fourth lens group remains stationary during zooming, andwherein, assuming that a maximum image height is IH, ConditionalExpression (4) is satisfied0.6<Bf/IH<1.2 ...   (4).
 2. The zoom lens according to claim 1, whereinConditional Expression (5-3) is satisfied0.23≤Bf/f4<0.3  (5-3).
 3. The zoom lens according to claim 1, whereinthe second lens group has, successively in order from the object side, apositive lens and the stop.
 4. The zoom lens according to claim 1,wherein the second lens group has a cemented lens comprising at leastone positive lens and at least one negative lens on the image side ofthe stop.
 5. The zoom lens according to claim 4, wherein the cementedlens consists of one positive lens and one negative lens, and whereinassuming that a difference between Abbe numbers of the positive lens andthe negative lens composing the cemented lens is Δνcd, ConditionalExpression (8) is satisfied15<Δνcd<60  (8).
 6. The zoom lens according to claim 5, whereinConditional Expression (8-1) is satisfied20<Δνcd<50  (8-1).
 7. The zoom lens according to claim 1, wherein thefourth lens group consists of a positive lens.
 8. The zoom lensaccording to claim 1, wherein the second lens group has a vibrationreduction lens group that performs vibration reduction by moving in adirection orthogonal to the optical axis, and wherein assuming that afocal length of the whole system during focusing on an object atinfinity at the telephoto end is ft, and a focal length of the vibrationreduction lens group is fois, Conditional Expression (6) is satisfied0.5<ft/fois<2  (6).
 9. An imaging apparatus comprising the zoom lensaccording to claim
 1. 10. The zoom lens according to claim 1, whereinConditional Expression (4-2) is satisfied0.6<Bf/IH≤0.81  (4-2).
 11. A zoom lens consisting of, in order from anobject side: a first lens group that has a negative refractive power; asecond lens group that has a positive refractive power; a third lensgroup that has a negative refractive power; and a fourth lens group thathas a positive refractive power, wherein during zooming, distancesbetween adjacent groups of the first lens group, the second lens group,the third lens group, and the fourth lens group in a direction of anoptical axis are changed, wherein the third lens group consists of anegative lens, wherein during focusing, only the third lens group movesalong the optical axis, wherein the second lens group has a stop, andhas lenses adjacent to the object side and the image side of the stop,wherein the second lens group has a cemented lens comprising at leastone positive lens and at least one negative lens on the image side ofthe stop, wherein the second lens group has a vibration reduction lensgroup that performs vibration reduction by moving in a directionorthogonal to the optical axis, wherein the vibration reduction lensgroup is arranged on the image side of the stop, wherein the fourth lensgroup remains stationary during zooming, and wherein assuming that aback focal length at the wide-angle end is Bf, and a maximum imageheight is IH, Conditional Expression (4) is satisfied0.6<Bf/IH<1.2  (4).
 12. The zoom lens according to claim 11, whereinassuming that a focal length of the whole system during focusing on anobject at infinity at the telephoto end is ft, and a focal length of thevibration reduction lens group is fois, Conditional Expression (6) issatisfied0.5<ft/fois<2  (6).
 13. The zoom lens according to claim 11, wherein thefourth lens group consists of a positive lens.
 14. The zoom lensaccording to claim 13, wherein the cemented lens consists of onepositive lens and one negative lens, and wherein assuming that adifference between Abbe numbers of the positive lens and the negativelens composing the cemented lens is Δνcd, Conditional Expression (8) issatisfied15<Δνcd<60  (8).
 15. The zoom lens according to claim 14, whereinConditional Expression (8-1) is satisfied20<Δνcd<50  (8-1).
 16. The zoom lens according to claim 11, wherein thecemented lens consists of one positive lens and one negative lens, andwherein assuming that a difference between Abbe numbers of the positivelens and the negative lens composing the cemented lens is Δνcd,Conditional Expression (8) is satisfied15<Δνcd<60  (8).
 17. The zoom lens according to claim 16, whereinConditional Expression (8-1) is satisfied20<Δνcd<50  (8-1).
 18. The zoom lens according to claim 16, whereinConditional Expression (8-2) is satisfied31.23≤Δνcd<60  (8-2).
 19. An imaging apparatus comprising the zoom lensaccording to claim
 11. 20. The zoom lens according to claim 11, whereinConditional Expression (4-3) is satisfied0.6<Bf/IH≤0.76  (4-3).